1. Field of the Invention
The present invention relates to a method for adhesion of electrodes, and more particularly to a method for adhesion of electrodes used on a lithium-ion secondary battery in which the method is convenient to apply on lithium-ion battery manufacturing process and improves the electrical capacitance of the battery.
2. Description of Related Art
Lithium-ion secondary batteries are widely applied to notebook computers, cell-phones, video-cameras, digital cameras, and other portable electrical products. As per the function improvement of these electrical products, the lithium-ion secondary battery is demanded to possess excellent capacitance but be minimized in size and weight.
The lithium-ion secondary battery in the early stage is made of the following acts of sandwiching two layers of isolation membranes between a positive electrode sheet and a negative electrode sheet; concentrically winding the laminated electrodes sheets with the isolation membranes to an electrode roll; inserting the electrode roll into a metal shell and pouring electrolyte solution into the metal shell; then sealing the metal shell to achieve the lithium-ion secondary battery.
Since the electrode roll has a volume with multiple vacant spaces inside the metal shell to reduce the capacitance, the electrode is piled up to an electrode block to reduce space-wasting inside the metal shell and to increase capacitance density (capacitance/volume(or weight)) of the battery. However, the technique of the electrode block is not matured enough to meet contemporary practice.
With regard to the metal shell, manufacturers use an aluminum shell to reduce the total weight of the battery because aluminum is lighter than other metals, but the aluminum shell is not sufficiently rigid to avoid deforming and easily causes damage of the electrode roll or electrode block inside the aluminum shell. Therefore, strongly laminating the electrode sheets and isolation layers is important. When the electrode sheets separate with the isolation layers, the charging and discharging characteristics of the battery are not stable and that seriously diminishes the lifetime of the battery. With regard to the electrode roll, achieving sufficient lamination of the electrodes sheets and the isolation layers is determined by an intensity of pulling force when winding. When the intensity of the pulling force is strong, the lamination of the electrode sheets and the isolation layers is excellent. However, strong pulling force easily causes breakage to the electrode sheets. Additionally, a redundant vacant space is left at center of the electrode roll after taking out a winding rod when the winding process is finished. Even when the electrode roll is squeezed in vacuum circumstance into the aluminum shell, the vacant space is still left to cause loss of capacitance density of the battery. With regard to the electrode block, because the electrodes sheets need polymer adhesive to stick with the isolation layers, the polymer adhesive makes the conductivity of the electrode sheet reduced.
There are three prior patents related to the present invention shown as following:
1. In granted EP933,824 patent, the method discloses the isolation layers are coated with adhesive or polymer adhesive to be laminated with the electrode sheets. However, the method of evenly coating adhesives on each isolation layers is complex and difficult to be carried out.
2. U.S. Pat. No. 5,723,231 discloses an electrolyte mixed of H3PO4 and a polymer such as poly-benzimidazole within a ratio range. The mixed electrolyte further contains forged silica oxide to increase adhesive efficiency of the mixed electrolyte to electrode sheets. However, sufficient lamination between the electrode sheets and the isolation layers still can not be achieved.
3. U.S. Pat. No. 5,470,357 discloses an electrolyte made of copolymer of vinylidene fluoride and hexafluoropropylene mixed with organic plasticizer applied on the electrode sheets to form an electrolyte membrane. Then, all the electrode sheets are laminated to compose a single battery. Lastly, a plurality of single batteries are combined together to form a lithium-ion secondary battery. Therefore, the producing process in 357′ patent is complex and only suitable to be applied on an electrode block.
To overcome the shortcomings, the present invention provides a method for adhesion of wound electrodes or electrode lamination for use in a lithium-ion secondary battery to mitigate or obviate the aforementioned problems.